Behaviour Of Self-compacting Concrete Research Articles

Effect of Colloidal Nano Silica as a Viscosity Modifying Agent in Self Compacting Concrete with High Volume POFA

This paper presents effects of Colloidal Nano Silica (CNS) as a Viscous Modifying Agent (VMA) on fresh properties of self-compacting concrete (SCC) containing high volume ground Palm Oil Fuel Ash (POFA). Accordingly, fresh properties of the SCC were tested using slump flow, J ring, L-box, and sieve stability test. To monitor the viscous behaviour of the fresh SCC with CNS, fillingability and passingability parameters were maintained within a desirable performance criterion whilst segregation, cohesiveness, and superplasticizer demand were the variables. All the mixtures were designed with the water/binder ratio of 0.45 and a total binder content of 500 kg/m3. The results revealed that the inclusion of CNS decreased the segregation and augmented the cohesion in all mixes.

Incorporation of fillers from marble and tile wastes in the composition of self-compacting concretes

The objective of this paper is to evaluate the incorporation of wastes from marbles and tiles factories as mineral additives to self-compacting concrete (SCC) and to substitute at 100% the known additions (limestone filler, fly ash, …). The use of these wastes can help produce economical self-compacting concretes (SCCW) and reduce the amount of wastes dumped into landfills. The influence of these wastes on the behavior of SCC in the fresh state is highlighted in comparison to a reference self-compacting concrete (SCCR) made with limestone filler while their effects on mechanical strength and ultrasonic testing are evaluated in the hardened state in comparison to the properties of both SCCR and an ordinary vibrated concrete (OVC). The compositions of the different concretes considered in the present study were formulated and optimized using the “Concrete LabPro2” software.The results of testing carried out on fresh concretes (slump flow test, V-funnel test, L-Box test and sieve stability test) show that the incorporation of wastes from marbles and tiles factories gives a satisfactory fluidity to the SCCW and their resistance to segregation, approaching those of SCCR. The mechanical properties of the tested concretes were evaluated by ultrasonic testing and by simple compressive testing and tensile splitting of cylindrical specimens (160mm×320mm) at the curing ages of 3, 7, 14 and 28days. The results show that the speed of wave propagation through the concrete and the compressive and tensile strengths are clearly sufficient for the self-compacting concretes incorporating wastes from marbles and tiles factories compared to those of SCCR and OVC.

Comparative Study on the Fatigue Behaviour of SCC and VC

Continuous cyclic loading on concrete constructions involves a progressive cracking mechanism, leading to significant changes of the material properties during the lifetime of the structure. Gradually, irreversible damage is inflicted and the carrying capacity is affected, which may cause structural collapse at a stress or strain level much lower than in case of a single static load. This so-called fatigue phenomenon is well-documented in literature for traditional, vibrated concrete (VC), but this is not the case for self-compacting concrete (SCC). Given the fact that this latter concrete type is already used worldwide in many types of structures, including cyclically loaded ones, a good knowledge and understanding of the static and fatigue material behaviour is crucial. Up till now, it is unsure whether SCC performs better, worse, or equally under fatigue loading conditions. Therefore, in this study, destructive four-point bending tests are performed on large beams, made from VC and SCC, both statically and cyclically (at different loading rates). A comparison of the deflection, strain, crack pattern and crack width evolution of the different concrete types is made. The results reveal some significant differences regarding concrete strain and crack width development during the cyclic tests.

Effect of cyclic loadings on heated self-compacting concrete

This experimental study examines the effect of cyclic loadings on heated self-compacting concrete (SCC). One hundred and eight standard cylindrical specimens and one hundred and eight cubic specimens were tested. Compressive strength of the concrete specimens was within the normal range with strengths of 25, 35, and 45MPa. Test speed was within the quasi-static range. The cyclic loading was imposed within the compressive area. The concrete specimens were heated to 23°C, 100°C, 200°C, 400°C, 600°C and 800°C and then were exposed to monotonic compressive loading or cyclic loading. The stress–strain diagram, compressive strength, and SCC behavior under the cyclic and monotonic loadings before and after heating were compared. The results show that the heated concrete has a lower compressive strength. The heated concrete exhibits more strains in the cyclic loading. Development of cracks in all the heated and unheated specimens under cyclic loading is different.

Mechanical Properties and Stress-Strain Behaviour of Hybrid Fibre-Reinforced Self-Compacting Concrete

Self-Compacting Concrete (SCC) is a highly flowable, self-levelling concrete. Just as in Fibre Reinforced Concrete (FRC), fibres can be incorporated into SCC also to get FRSCC. In the present study hybrid fibres namely, Polypropylene and hooked ended Steel fibres are incorporated in different volume fractions and their fresh and hardened state properties have been studied. Fly ash and Silica Fume obtained as waste from industries are used as replacement for cement, the replacement being 10% and 5% respectively. The behaviour of HFRSCC under compression, tension and flexure has been experimentally observed. The stress-strain behaviour of SCC and HFRSCC have also been studied by varying the combinations of volume fractions of hybrid fibres.

Characterization of heat-treated self-compacting concrete containing mineral admixtures at early age and in the long term

Self-compacting concretes (SCCs) are increasingly used in the field of prefabrication, although the final strength of the heat-treated concrete is less than that of reference samples that have been cured in normal conditions. The aim of this work is to contribute to the improvement of the mechanical behavior of this kind of SCC. This paper presents the effect of the incorporation of local mineral admixtures on the behavior of heat-treated SCC at an early age (1day) and in the long term (28 and 180days). The characteristics of the SCC in the fresh and hardened states were also studied. The adopted heat-treatment cycle attained a maximum temperature of 60°C and a total duration of 24h. Three additions to the cement at the levels of 20% and 40% were used. They were fine limestone (LF), granulated slag (GS), and crystallized slag (CS). The fresh states characteristics of SCC are affected by the nature and dosage of the mineral admixture. In the hardened state, the comparison between the elaborated SCC and the control SCC without addition and without heat treatment showed an overall gain in strength at early age and minimal loss in the long term. The CS with a dosage of 40% allowed to the heat-treated SCC to be the less porous and the more resistant one compared to the elaborated SCCs. The use of LF appears to be more favorable if its incorporation is limited to below 20%. The GS is also favorable with 20% and it can be more beneficial if its fineness exceed that of the cement powder.

Rheology and mechanical characteristics of self-compacting concrete mixtures containing metakaolin

Metakaolin is a supplementary cementing material (SCM), which has been recently used in Self-Compacting Concrete (SCC). This study investigates the effect of replacement of cement or limestone powder by metakaolin, on the rheology and the mechanical characteristics of the concrete mixtures. It has been found that the rheological behaviour of SCC is affected by the incorporation of metakaolin. Yet, this effect is not always traceable in the assigned rheological classes. The compressive strength is significantly enhanced and a similarly increasing trend is observed for higher replacement levels, regardless of the replaced material. A lower but still considerable improvement of the tensile strength is also evident. Finally, code or literature curves for NVC tend to overestimate the tensile strength for SCC.

A comprehensive investigation into the effect of water to cement ratio and powder content on mechanical properties of self-compacting concrete

Self compacting concrete (SCC), as an innovative construction material in concrete industry, offers a safer and more productive construction process due to favorable rheological performance which is caused by SCC’s different mixture composition. This difference may have remarkable influence on the mechanical behavior of SCC as compared to normal vibrated concrete (NVC) in hardened state. Therefore, it is vital to know whether the use of all assumptions and relations that have been formulated for NVC in current design codes are also valid for SCC. Furthermore, this study presents an extensive evaluation and comparison between mechanical properties of SCC using current international codes and predictive equations proposed by other researchers. Thus, in this experimental study, key mechanical properties of SCC are investigated for sixteen SCC mixes with different w/c ratios and different powder contents. In the present study, an extensive data reported by many researchers for SCC and NVC has been used to validate the obtained results.

Thermal performance of self-compacting concrete: destructive and nondestructive evaluation

Recently, self-compacting concrete (SCC) has been increasingly used in high-rise buildings and industrial units, susceptible to accidental fires. The probable degradation of these structures necessitates understanding SCC behavior under elevated temperatures. For this, an extensive experimental investigation was undertaken to evaluate the effect of elevated temperature (300–600 °C) on the mechanical compressive properties of SCC; considering the effect of water-to-cement ratio (0.40–0.50), type of mineral aggregate and filler (limestone and basalt), and internal humidity. Standard cylinder (150 mm × 300 mm) and prism (100 mm × 100 mm × 300 mm) specimens were prepared from various SCC mixtures, cured for 28 d in limewater, and then stored at different environments for an additional 90 d to create varying internal humidity levels; ranging from 28 to 95%. Later, specimens were subjected to elevated temperatures in an electrical furnace, then cooled and tested for compressive mechanical response or non-destructively using resonance frequency, ultrasonic pulse velocity, and rebound hammer evaluation techniques. The results showed significant reduction in residual compressive strength, and elastic modulus, and an increase in compressive strain at peak stress and toughness as elevated temperature was increased. The SCC mixtures at upper water-to-cement ratios with basalt aggregate showed higher resistance to elevated temperatures than corresponding ones with limestone. Internal humidity in SCC had a detrimental impact on compressive strength and elastic modulus; especially at exposure temperatures below 400 °C. The statistical correlations between residuals for compressive strength or elastic modulus and nondestructive damage indices can be classified as very good. Furthermore, the nonlinear empirical models, developed to predict residuals for compressive strength and elastic modulus in terms of the study parameters, showed relatively high prediction potential, hence are recommended to be used in designing SCC mixtures for best resistance against possible fire attack.

The effect of aging on the fracture characteristics and ductility of self-compacting concrete

Good knowledge of fracture parameters and cracking behavior of self-compacting concrete (SCC) from early ages until the SCC becomes mature plays an important role in design of SCC structure and also in evaluation of durability and consequently prevention of damage. In this paper, variation of fracture parameters and corresponding ductility behavior of SCC at different ages (e.g. 3days, 7days, 28days and 90days) for SCC mixes with w/c ratios of 0.45 and 0.65 have been experimentally studied. To do so, three-point bending tests were carried out on 120 notched beams. Then, size effect method (SEM) and work of fracture method (WFM) were applied to interpret the results. The results of analyses indicated that as the concrete is aging from 3days to 90days: (a) fracture energies from SEM (Gf) and WFM (GF) are increased: (b) effective size of the process zone (Cf) in SEM and characteristic length (Lch) in WFM are considerably decreased indicating increase of concrete brittleness: (c) fracture surface of concrete passing through the aggregate is increased which is attributed to strength improvement of hardened cement paste and aggregate–paste transition zone: (d) fracture toughness is significantly increased: (e) brittleness number is almost doubled. Also, the ratio of GF/Gf, which is applied for calibration of numerical models of cracking at different ages, is equal to 2.70.

Creep and Shrinkage of Self-Compacting Concrete with and without Fibers

Fiber-reinforced self-compacting concrete (FRSCC) is a high-performance building material that combines positive aspects of fresh properties of self-compacting concrete (SCC) with improved characteristics of hardened concrete as a result of fiber addition. Considering these properties, the application ranges of both FRSCC and SCC can be covered. To produce SCC, either the constituent materials or the corresponding mix proportions may notably differ from the conventional concrete (CC). These modifications besides enhance the concrete fresh properties affect the hardened properties of the concrete including creep and shrinkage. Therefore, it is vital to investigate whether all the assumed hypotheses about conventional concrete are also valid for SCC structures. In the present paper, a numerical and experimental study about creep and shrinkage behavior of FRSCC and SCC is performed. Two new creep and shrinkage prediction models based on the comprehensive analysis on the available models of both CC and SCC are proposed for FRSCC and SCC structures. In order to evaluate the predictability of the proposed models, an experimental program was carried out. For this purpose, four SCC mixes plain SCC, steel, polypropylene, and hybrid FRSCC are considered in the test program. Several specimens were loaded and deformation in non-loaded specimens was also measured to assess shrinkage. All specimens were kept under constant stress during at least 364 days in a climatic chamber with temperature and relative humidity of 22oC and 50%, respectively. Results showed that the new models were able to predict deformations with good accuracy, although providing deformations slight overestimated.

Fracture Toughness and Cracking Behaviour of SCC Compared to VC

Vibrated concrete (VC) and self-compacting concrete (SCC) have a substantially different composition, resulting in dissimilar mechanical properties regarding cracking behaviour. The critical value of the mode I stress-intensity factor KIC is an appropriate fracture parameter for evaluating fracture toughness and can be obtained from three-point bending tests (3PBT) on small, notched specimens. Subsequent determination of the energy release rate thus allows to examine the crack propagation and fracture process of both concrete types. This paper describes the results of such 3PBTs on samples, made from VC and SCC. Evaluation of the cracking behaviour, derived from these results, reveals remarkable differences.

Flexural and shear behavior of steel fiber reinforced SCC beams

This paper deals with the effect of steel fiber reinforcement on the behavior of Self-Compacting Concrete (SCC) beams. Bending tests were carried out to examine the effect of low fiber content (0.25% by volume) on the flexural behavior of beams with different amounts of steel rebar reinforcement. The study compares the behavior of reinforced concrete beams cast either with control SCC and the one of Fiber-Reinforced Self-Compacting Concrete (FRSCC). Fibers used were made of stainless amorphous metal. Their influence was studied through the global and local mechanical responses of the beams. The results show that fiber reinforcement allows the control of cracking to be improved. Yielding, ductility and load bearing capacity are not modified by the fiber reinforcement; its effects are limited to the kinetics and distribution of cracks. If it was observed that the used fiber content reduced stresses in the stirrups, they could not be considered as a solution to replace stirrups. However, their ability to transfer tensile stress through a crack provided greater beam stiffness, notably with a low steel bar reinforcement ratio. It was concluded that stainless steel fiber reinforcement is a suitable solution to control crack width in reinforced concrete elements in aggressive environments with respect to the limitations imposed by design codes such as the European code Eurocode 2.

Effect of Grade of Concrete on the Performance of Self-Compacting Concrete Beams Subjected to Elevated Temperatures

Self-compacting concrete (SCC) is a new generation concrete that consolidates without any external effort. Due to its advantages over the conventional concrete, the usage of SCC increases day by day. Understanding the behaviour of SCC is important in the design of structures subjected to elevated temperature. A study was carried out to understand the behaviour of SCC beams of various grades exposed to elevated temperatures under flexural loading. The beams were exposed to a temperature of 900°C. The heated specimens were cooled either by air or water. The research work was carried out for different grades of concrete. It is found from the results that the loss of strength of SCC beams of higher grades was more than that of the lower grade SCC beams. It was also found that the reduction in compressive, tensile and flexural strength of the specimens depends on type of heating and cooling conditions.

Effect of Clay Fines on the Behavior of Self-Compacting Concrete

The technology of concrete has significantly increased in recent years through the use of super plasticizer and availability of mineral additions. One of the most recent materials used as an additive, replacing a portion of cement in concrete, is fine clay fired at a temperature of 800℃ to 900℃. This research is based on trials that complied with artificial pozzolan (waste crushed brick), and their effect on the rheological and mechanical behavior of mortar. The addition of 5% of a waste crushed brick has helped not only to improve the strength (tensile and compression), but also to foster a better rheological behavior in terms of fluidity and stability, with a low heat of hydration compared to control. However, tests of optimizing the content of self-compacting concrete (SCC) in coarse aggregates, sand and binder, led us to confirm that the combined mass of more optimal (better workability and stability) is that based on low in volumetric percentage of sand/paste with a granular skeleton richest gravel low dimensions (2/3 of G 3/8 and 1/3 of G 8/15).

Numerical Analysis for Drying Creep Behavior of Self-Compacting Concrete

Drying creep of self-compacting concrete (SCC) has two different sources: microcracking and stress-induced shrinkage. Based on theory for pore water and microcracking theory of concrete, the model for drying creep caused by constant stress is derived from rheological equations. The proposed model is coupled with FEM analysis by recursive calculation, so that the creep caused by changing load can be calculated without considering stress history. Verification of the model is conducted through comparison with experimental result and Bazant’s empirical model. The comparing results validate the model for drying creep of SCC.

An empirical approach for the optimisation of aggregate combinations for self-compacting concrete

The fresh and hardened properties of self-compacting concrete (SCC) depend on number of factors such as paste composition, paste content, aggregate content, aggregate gradation etc. In the present investigation, the influence of the packing density of aggregates on the properties of SCC was evaluated. Experiments were conducted to measure the packing density for different combinations of aggregates precisely. A ternary packing diagram (TPD) was developed based on the packing density of measured and interpolated data. Considering the limitations in generalising the TPD and the difficulty involved in adopting mathematical models for aggregates, an attempt was made to establish a simple method for the selection of the combination of aggregates resulting in maximum packing density from the particle size distribution of aggregates (represented by the Coefficient of uniformity—C u). Further, studies were extended to investigate the effect of aggregate packing density on fresh and hardened SCC properties. The results indicate that for a constant paste volume and paste composition, with increase in packing density of aggregates, the fresh properties and the compressive strength of SCC were improved positively. An attempt was also made to identify the influence of 10 different proportions of aggregates having the same packing density on the properties of SCC. The results indicate that at the same aggregate packing density, the fresh concrete properties were influenced significantly by the choice of the aggregate combination, while there was little or no influence on the hardened properties. Furthermore, the experimental data obtained was used for supplementary validation of the existing model (compressible packing model) for predicting the packing density and the fresh behaviour of SCC.

Self-compacting concrete incorporating filler additives: Performance at high temperatures

An experimental investigation was conducted to evaluate the performance of self-compacting concrete (SCC) subjected to elevated temperatures. For this purpose, Portland cement (PC) was replaced with limestone powder (LP), basalt powder (BP) and marble powder (MP) in various proportioning rates. Half of the total specimens for each mix type were studied by adding polypropylene (PP) fibers to improve the understanding of the effect of PP fibers on the behavior of SCCs subjected to high temperatures. SCC mixtures were prepared with water to cement ratio of 0.33 and polypropylene fibers content was 2 kg/m 3 for the mixtures containing polypropylene fibers. Specimens were heated up to elevated temperatures (200, 400, 600 and 800 °C) at the age of 56 days. Then, tests were conducted to determine loss in weight and compressive strength. Moreover, the change of ultrasonic pulse velocity (UPV) was determined and surface crack observations were made after being exposed to elevated temperatures. Experimental results indicate that a severe strength loss was observed for all of the SCC mixtures after exposure to 600 °C, particularly the concretes containing polypropylene fibers though they reduce and eliminate the risk of the explosive spalling. At higher replacement levels of LP, BP and BP further lower resudial strength was observed. In terms of percent residual properties, control mixture specimens performed better than filler additive specimens for all heating cycles.

Flexural capacity predictions of self-compacting concrete beams using stress–strain relationship in axial compression

Due to its unique composition, self-compacting concrete (SCC) may have stress–strain characteristics that are significantly different from those of conventionally vibrated concrete (CVC). An experimental investigation was carried out to generate complete stress–strain curves for SCC in axial compression by testing 162 standard cylindrical specimens of strength 35–70 MPa. The accuracy of analytical models for CVC selected from the literature in predicting the stress–strain behaviour of the SCC mixtures is discussed and their inadequacies are highlighted. A new constitutive model covering a wide range of concrete strengths is proposed for SCC. The equivalent rectangular stress block specified in current design codes for flexural capacity predictions was developed on the basis of tests on CVC; given the observed differences in the stress–strain behaviour of CVC and SCC, its applicability to structural design of SCC members becomes questionable. On the basis of the proposed constitutive model for SCC, a new equivalent rectangular stress block valid for concrete strengths of up to 70 MPa is presented for analysis of flexural capacity. The flexural capacity predictions of the proposed stress block are compared with experimental data from the present work and other investigations reported in the literature, and good agreement was obtained. A simple analytical approach is presented for predictive assessment of the load–deflection behaviour of SCC beams with a reasonable degree of accuracy.

Effect of mineral admixture on resistance to sulphuric and hydrochloric acid attacks in self-compacting concrete

This paper presents a detailed experimental investigation of the acid resistance of economical self-compacting concrete (SCC) prepared with natural pozzolan, immersed for up to 12 weeks in sulphuric acid (H2SO4) and hydrochloric acid (HCl) solutions. The results are compared with those from a control concrete and other SCCs prepared with fly ash and limestone filler. The different factors considered in this study were the effect of mineral admixture type and the strength classes (30, 50, and 70 MPa) of the concrete specimens. In total, 12 formulations were tested. Mass and compressive strength losses are the main properties investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were used to better understand the kinetics of deterioration of each type of concrete. The results show the positive influence of natural pozzolan on the behaviour of SCC under both sulphuric and hydrochloric acid mediums.